The signs a battery is failing before it stops working
A battery that is about to die usually shows warning signs days or weeks before it quits completely. The most common sign is that a device holds a charge for much less time than it used to — a phone that used to last a full day now dies by afternoon, or a laptop that ran for six hours now shuts down after two. Another early warning is that the device gets noticeably hot during normal use, especially near the bottom or back where the battery sits. A third sign is that the battery percentage jumps around erratically: it might show 40 percent, then suddenly drop to 5 percent, then climb back up to 25 percent without you doing anything.
On some devices, the operating system itself will warn you. iPhones show a red battery icon and a "Low Battery" message when the charge drops below 20 percent, and at very low charge they may shut down unexpectedly even though the percentage shows higher than zero. Android phones display similar warnings, though the exact message depends on which version you have. Laptops running Windows or macOS will show a notification in the system tray or menu bar saying the battery health is degraded or that you should service the battery soon.
Key Takeaways
- A battery nearing the end of its life will hold a charge for significantly less time than when the device was new, often dropping to half the original runtime within a few months.
- Unexpected heat during normal use, especially concentrated near the battery location, is a sign the battery chemistry is breaking down and may fail soon.
- Battery percentage that jumps erratically or drops suddenly to zero even when showing 20 or 30 percent remaining indicates the battery can no longer report its state accurately.
- Most phones and laptops display built-in warnings when battery health degrades, and checking the battery settings menu will show you the current health percentage.
How to check battery health on your phone
On an iPhone, go to Settings, then Battery, then Battery Health & Charging. You will see a number labeled "Maximum Capacity" — this shows what percentage of the original charge the battery can now hold. A new iPhone battery shows 100 percent. When it drops below 80 percent, Apple considers the battery degraded. When it falls below 50 percent, the phone may shut down unexpectedly even when the percentage display shows higher charge remaining.
On an Android phone, the process varies by manufacturer. Samsung phones: go to Settings, then Battery and Device Care, then Battery, then Battery Health. Google Pixel phones: go to Settings, then Battery, then Battery Health. Other Android brands may bury this information in different menus or not display it at all — if you cannot find it in Settings under Battery or Device Care, your phone may not have a built-in health display. In that case, you can read a free app like Accubattery from the Google Play Store, which monitors your battery over time and estimates its health.
How to check battery health on a laptop
On a Windows laptop, right-click the battery icon in the system tray (bottom right corner of the screen) and select "See more details" or "Power settings." This opens the Battery settings page. Scroll down to find "Battery health" or "Battery report." If you see a "Battery report" button, click it — Windows will generate a detailed report showing the design capacity versus the current full-charge capacity. If the current capacity is significantly lower than the design capacity, the battery is degrading.
On a Mac, hold the Option key and click the battery icon in the menu bar (top right corner). A dropdown menu will appear showing the battery's condition. It will say either "Normal," "Replace Soon," "Replace Now," or "Service Battery." If it says anything other than "Normal," the battery is failing or has already failed. You can also generate a detailed report by holding Option, clicking the battery icon, and looking for a "Condition" line that shows the current status.
Why batteries degrade over time
All rechargeable batteries lose capacity with age and use because the chemical reactions inside them become less efficient. Every time you charge and discharge a battery, the materials inside break down slightly. After hundreds or thousands of charge cycles, enough material has degraded that the battery can no longer hold as much energy. This is not a defect — it is how battery chemistry works, and it happens to every rechargeable battery eventually.
Heat accelerates this process significantly. A battery that spends most of its time in a hot environment will degrade much faster than one kept cool. This is why leaving a phone in a hot car or running a laptop without proper ventilation shortens battery life. Cold also slows chemical reactions, which is why batteries seem to drain faster in winter, though cold does not permanently damage them the way heat does.
What to do when a battery is dying
If your device is still under warranty, contact the manufacturer. Apple, Samsung, Google, and most laptop makers will replace a battery that has degraded below a certain threshold, usually at no cost if the device is within one to two years of purchase. Check your device's warranty status on the manufacturer's website by entering your serial number.
If your device is out of warranty, you have two options: replace the battery or replace the device. Battery replacement costs vary widely. On an iPhone, Apple charges between $50 and $100 depending on the model. On a Samsung phone, third-party repair shops often charge $30 to $80. On a laptop, replacement can cost $100 to $300 depending on the model. If your device is several years old, the cost of a new battery might approach the cost of a used replacement device, so compare prices before deciding.
How to extend battery life and slow degradation
Keep your device cool. Avoid leaving phones or laptops in direct sunlight, in cars on hot days, or in enclosed spaces without ventilation. If your device gets hot during use, close unnecessary apps or programs and give it a break. For laptops, use a cooling pad or may support the vents are not blocked by dust or fabric.
Avoid letting the battery drain completely to zero regularly. Lithium batteries, which power most phones and laptops, prefer to stay between 20 and 80 percent charged. If you can, charge your device when it reaches 20 percent rather than waiting until it shuts down. Similarly, unplug it when it reaches 80 or 90 percent rather than leaving it plugged in all night. Some newer phones and laptops have an "Optimized Battery Charging" or "Adaptive Charging" feature that learns your charging habits and slows charging after 80 percent to reduce wear — enable this if your device offers it.
Reduce screen brightness and disable features you do not use. Brightness is one of the largest drains on battery power. Turning off Bluetooth, location services, and background app refresh when you do not need them extends the time between charges, which means fewer charge cycles and slower degradation.
Frequently Asked Questions
Can I replace a battery myself?
On some phones and laptops, yes, but it requires opening the device and is risky if you have not done it before. iPhones and most modern Samsung phones have batteries glued in place, making self-replacement difficult without damaging the screen or other components. Older phones and some laptops have user-replaceable batteries that straightforward slide out. If you want to try, search for a teardown guide specific to your model on iFixit.com, which shows exactly how to open your device and what tools you need.
Does leaving my phone plugged in overnight damage the battery?
Modern phones and laptops are designed to stop charging once they reach 100 percent, so leaving them plugged in does not overcharge them. However, keeping a battery at 100 percent constantly does cause slow degradation over time. If you charge overnight regularly, enable "Optimized Battery Charging" in your settings — it will charge to 80 percent overnight and finish the last 20 percent shortly before you wake up, reducing wear.
Why does my battery percentage jump around?
When a battery is failing, it cannot accurately report how much charge it holds. The battery management system guesses based on voltage, but a degraded battery's voltage becomes unreliable, causing the percentage to fluctuate. This usually means the battery is near the end of its life and should be replaced soon to avoid unexpected shutdowns.
Is it safe to use a device with a failing battery?
A failing battery is not dangerous in the sense that it will not explode or catch fire under normal use — modern devices have safety circuits that prevent that. However, a failing battery can shut down your device suddenly without warning, which could cause problems if you are in the middle of important work or navigation. It is better to replace it before it becomes unreliable.